The certification process is the biggest reason I can't 100% back Crossfit as a whole. I've heard that in a weekend you can get certified in a specific catagory, like say Kettlebells. Alot of the times they have a certain test, normally a specific workout, that the potential instructors have to pass. But instead they end up essentially passing everyone. Plus just because you are fit enough to do complete some set up physical activity doesn't mean you are qualified to instruct someone else. I think a written test needs to be done as well and the classes should be entirely longer than a weekend. (i know not all are just weekenders).
I don't post in lifting forums but i've read alot of articles that tell people to stay away from Crossfit. They are big on circuits and pushing the body to its absolute breaking point with every single exercise. It doesn't take a genius to know that you already need to be in a certain shape in order to have your body perform like that. The problem with Crossfit is, alot of instructors thrust people who probably haven't lifted more than the remote in the last few years, right into the thick of things. I'm not some supreme physical specimen but i know that the average couch potato isn't going to be able to handle a 1/4 of what i can do. It's this type of practice that is dangerous.
Now on the flipside i have heard some great articles on the program and have participated in some of their workouts myself. They can be awesome and really be good for you if you are already in shape and preparing for something specific. I used them to help me with my conditioning for a fight. I don't know if it was the absolute solution but i feel that they helped alot. I've also worked out with instructors that fully know that everyone is not equal and don't force everyone to do the exact same workout (weight/reps) and modify for the individual for their needs and abilities.